[positiveion]

2-hydroxybenzoic acid + Ethanoic acid --> Aspirin + Water

2C7H6O3 + C4H6O3 --> 2C9H8O4 + H2O

15. g of 2-hydroxybenzoic acid and 15.0 g of ethanoic acid given.

Calculate the mass of aspirin that could be obtained in this reaction.

My working:

2C7H6O3
given: 15.0g
1 mole: 276.26g

C4H6O3
given: 15.06
1 mole: 102.1g

2C7H6O3 is the limiting reagent, so I do the ratio calculations with it.

552.52 : 360.34 = 15 : x
(2 moles of 2-hydroxybenzoic acid to 2 moles of aspirin equates to the given 15 g of 2-hydroxybenzoic acid to the unknown aspirin mass)

552.52/360.34 = 15/x
x(552.52)=15(360.34)
x = 5405.1/552.52
x = 9.782632303

But thats wrong because the answer is 19.6
..

Could you tell me where I went wrong?

[Tin Man]

2C7H6O3 + C4H6O3 --> 2C9H8O4 + H2O

2C7H6O3
given: 15.0g
1 mole: 276.26g

I haven't fully checked your work, but I'd look at this here.

The "2" in front of the molecule is a coefficent, representing the mole ratio of this molecule to the rest of the equation. Like I said, I didn't run through your whole equation and check your numbers, but if I were to guess a point where you may have messed up, it would probably be here. You're saying that you have ONE mole of TWO moles of the substance, which is going to make things complicated for you.

One mole of C₇H₆O₃ is 138.06g, half of your answer. Two moles is 276.26g. For every two moles of C₇H₆O₃, you have one mole of C₄H₆O₃, two moles of C₉H₈O₄, and one mole of H₂O.

Does that help?

[positiveion]

Yes thank you so much!

[positiveion]

But I am also unsure about how to do the follow up question which is:

if the mass obtained in this experiment was 13.7g, calculate the percentage yield of aspirin.

I had though it would be the grams of aspirin and water added together,

so 2C9H8O4 = 360.32 grams and H20 = 18.02 grams

360.34 + 18.02 = 378.36

360.34/378.36 = 0.9523

Therefore 95%

The answer however is 69.9% and I don't know what I did wrong.

[DrCMS]

You did not work out the %yield is the problem. 

I have no idea what you think you're working out.

% yield = actual yield/theoretical yield

[positiveion]

How do you find the theoretical yield?

[Borek]

From stoichiometry.

[DrCMS]

How do you find the theoretical yield?

What do you think you calcuated it in part 1?

[positiveion]

okay how do you find the actual yield, then?

[Borek]

With balance.

[DrCMS]

okay how do you find the actual yield, then?

You are given it in part 2 - the actual yield is 13.7g. 

(rant deleted)